Tape surface damage near the edge of the tape is a leading cause of data loss and tape cartridge failure. Additionally, tape contact with tape guides can contribute to debris generation and to a malformed tape pack. Large radius stationary cylindrical tape guides have been frequently used to transport tape with minimal physical tape-to-guide contact, and in particular, to reduce tape surface contact near the edge with the tape guide.
The use of a flying tape guide helps to reduce the tape-to-guide friction and consequently tape wear. A flying tape guide causes the tape to fly (at specific tape speed and tension) over the bearing surface of the tape guide. When operated at the designed speed and tension, there is almost no physical contact between the moving tape and the stationary tape guide. At lower tape speeds or higher tape tension, however, tape lift is reduce and there is generally tape surface contact pressure along the tape edges.
Flying tape guides, however, do not necessarily prevent tape surface contact at the edges. FIG. 1 is a schematic end view of a flat flying tape guide 300. The cross-web tension is generally uniform over the length of the guide 304. Under constant tape tension, however, the spacing between moving tape 302 and stationary tape guide 304 is not uniform across the width of the tape 302. The spacing along edges 306, 308 of the tape 302 is generally less then the spacing near the center 310 due to atmospheric pressure acting on the tape edge 306, 308, anticlastic tape deformation and side leakage 312 of the air bearing surface. The problem of tape edge damage will become more severe as the magnetic tape industry moves to thinner media where the cross-web bending rigidity of the tape is significantly reduced.
In both belt-driven and hub-driven tape cartridges, the allowable tape speed and storage capacity (i.e., data density) increase with the accuracy at which the tape is coupled with the read/write heads. Therefore, any solution to the problem of tape edge damage that alters tape-to-head interface will likely have a direct impact on tape drive performance. For example, tape cartridges must meet minimum tape tension specifications while simultaneously maintaining minimum drive force specifications. The tape tension must not fall below a certain level as the tape passes from reel to reel. Otherwise, contact between the read/write head and the tape will be insufficient. The minimum achievable tape tension should be sufficiently high to ensure proper cartridge operation. Similarly, the maximum required frictional drive force should be as low as possible to enhance cartridge operation within the power limitations of the drive motor. Thus, there is a limitation on the frictional drive force. The frictional drive force is that portion of the drive force which affects power loss at the interface between the backside of the tape and the tape guide. Minimizing the frictional drive force and improving tape tracking can be accomplished by minimizing the friction at the interface between the tape and the tape guides, which accounts for approximately one-third of the drive force in a data cartridge.